1. Field of the Invention
The present invention relates to a process and apparatus for sterilizing materials and products including foodstuffs, more particularly to improvements in the method of sterilization of spices and dry herbs. In addition, this invention relates to an apparatus and method which achieves better control of the sterilization process, allows for much easier cleaning, and results in a more satisfactorily sterilized product.
2. Description of the Related Art
It has been known for many years that sterilization of grains was necessary in order to reduce microbial counts to a satisfactory level. In fact, for wheat grain, a microbial count of less than 5,000 per gram is necessary to prevent deterioration of refrigerated doughs for biscuits, dinner rolls, cookies, pizza, coffee cake and the like. This level differs quite markedly from typical counts of 100,000 or higher prior to treatment.
Paralleling the need for reducing the microbial counts in grains, the spices and herbs which are important ingredients in these convenience and fresh refrigerated foods must also be sterilized in order to avoid microbiological spoilage of these foods.
Methods which have been employed to reduce microbial populations include washing, heating, treating with fumigants, disinfectants, or chemical sterilants; irradiation with ultraviolet light; exposure to ozone; radio frequency or dielectric heating; treatment with sonic and supersonic vibrations; and irradiation with gamma rays, electron beams, or X-rays. Treatment with ethylene or propylene oxide has also been effective but has come under great scrutiny by governmental agencies, requiring reduction of residual chemical in the product by repeated cycles of aeration, heating, and evacuation. In fact, sterilization with ethylene oxide has been forbidden in some European countries because of it's toxic nature.
Heating as a means of controlling microbial population has advantages over other methods in that no chemicals are added to the product, no food regulations are involved, whole spices and herbs of high microbiological population can be treated effectively, and equipment for treating is conventional and readily available. The major drawback to using raw heat for sterilization is that substantial losses of volatile oils can occur or the product can easily be burnt, causing a flavor change, if exposed to the heat for too long or to an excessive temperature.
Traditionally, these treatment methods have been carried out in batches where part of the processing time was consumed in filling, removing, and cleaning. Additionally, unless all of the variables were very closely controlled between batches, the batches would differ from each other.
Further improvement in the method of treatment to reduce microbial (bacterial and fungal) counts centered around treatment by dipping in a hot solution of sanitizing agent, by indirect steaming, and by direct steaming.
Direct steam contact sterilization methods which have developed included continuous processes such as tubular screw conveyors where the product and the steam are introduced together and transferred the length of the screw conveyor. Shortcomings of this method include low capacity and the necessity for a steam-heated double jacket that is required to prevent the formation of condensation on the walls of the trough. Further, the inherent design of screw conveyors results in some unavoidable product damage because of the "pushing" effect on the product by the transfer mechanism.
Another direct steam sterilization method which developed involved use of a rotating drum with baffles creating a fluidized bed process. The throughput of this process improved over earlier designs but the residence time of the product with the steam could not be precisely controlled, allowing for undesirable results.
These high temperature short time (HTST) treatments with steam pressure has been shown to be an effective sterilization process for spices and herbs, producing a satisfactory product from a bacteriological, as well as other (color, flavor, etc.), point of view.
During this sterilization process the moisture content of the spice or herb increases due to the direct steam infusion and condensation of the steam vapor on the product. In order to avoid microbiological spoilage of the product due to this higher moisture content, the product typically has to be dried and cooled after the process.
U.S. Pat. No. 3,994,685 discloses a two-stage process where material to be sterilized is rapidly and uniformly heated to the desired temperature while being vigorously mixed with the sterilizing agent by means of a mechanical agitator. In the second stage of this process, the material is kept at the desired sterilization temperature for a predetermined length of time, remaining virtually stationary since no mechanical devices such as stirrers or mixers are employed in this stage. This Patent discloses that the second stage may include multiple layers of material that correspond to the individual batches introduced from the first stage. The Patent also discloses that the material is to be removed from the second stage by gravity means where each layer of material corresponding to a batch from the first stage is removed after the appropriate treatment time. In practice, because of uncontrollable variations in the gravity flow, the second stage treatment time can vary, thus it is possible that some portions of the product will remain unsterilized. In addition, since the material remains in an unagitated state and in contact with steam for some period of time in the second stage, caking, nesting, and material buildup on the container walls will be difficult to prevent.
U.S. Pat. No. 4,563,263 discloses a continuous sterilization and cooling apparatus and method. In this Patent, the pressurized steam treatment chamber is directly coupled to a pressurized cooler where hot material that has been discharged from the treatment chamber is cooled by direct contact with a coolant fluid. The object of this invention was to provide an apparatus and method for removing particulate matter from a pressurized steam treatment chamber while preventing flashing, disintegration, attrition, and mushing. It is apparent that the drawbacks of this disclosure include difficulty assuring that each particle of the product was treated for only the proper length of time at the right temperature. Additionally, this apparatus contains many moving mechanical parts which make effective and efficient cleaning very difficult.
U.S. Pat. No. 4,844,933 discloses a process and apparatus for sterilization of spices and leafy herbs where culinary steam is injected into a vessel while the contents are being mechanically agitated by an array of paddles. The process is a batch operation where the material is first introduced into the vessel, sterilizing steam is introduced into the vessel and the material is exposed to this steam for a predetermined time. When this time limit has been achieved, the material is transferred to a second adjoining vessel where it is cooled. Transfer of the material between the various vessels is achieved through pressure differentials. The methods employed to transfer and sterilize the product involve substantial physical manipulation which may tend to change the nature of the product. Additionally, product can collect in various corners of the equipment making cleaning relatively difficult.
In summary, various continuous process sterilization methods are already known. Some devices utilizing these methods contain baffles designed to insure that the product being treated remains in the apparatus for the minimum length of time needed for sterilization. Other designs depend on a fluidized bed to transfer the product through the treatment apparatus. However, in practice, the treatment time cannot be guaranteed since particles may pass through the apparatus quicker than intended resulting in inadequate sterilization. Also, the converse may occur where the particles remain in the apparatus longer than intended causing undesirable changes to the qualities of these particles. Additionally, many of the steam sterilization methods are utilizing wet steam which requires higher pressures and longer treatment time. For all steam treatment processes presently known, cleaning can only be accomplished by either opening access plates or disassembling the apparatus to remove residual particles for a changeover to a different material.
3. Objects of the Invention
Accordingly it is an object of the present invention to provide an improved continuous sterilization method and apparatus for spices, herbs and the like.
A further object of the invention is to provide a sterilization method and apparatus wherein the contact time of the material with the hot gas is effectively and very closely controlled thus optimizing the sterilization through processing every particle for the same period of time while concurrently minimizing undesirable side effects such as flavor change and allowing for exact repeatability between loads.
Another object is to agitate the material adequately as it is being sterilized so that sterilization can be accomplished efficiently, reliably, and thoroughly.
Another object is to provide an apparatus that minimizes the physical damage to the material as it is being processed.
Still another object is to utilize gravitational force to move the material through the apparatus.
Another object is to provide a process and apparatus where the environment and time required to process can be easily changed to suit the requirements of the material being processed.
Still yet another object is to design an apparatus that achieves positive and continuous cleaning as well as vastly shortened time for cleaning during a changeover.
Another object is to utilize the latent heat of steam for the sterilization process.
Yet another object is to design an apparatus which can be utilized to efficiently sterilize many different spices and herbs with easy changeover and minimal cleaning.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the, following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.